If the parents check out, it wouldn't bother me. I'd be clear on what I expect of them...cleaning wise...and if he had a lease...perhaps have them pay for the inbetween days (hopefully they would be next to nothing if little work needed to be done).
Thanks for your response, Kristina! It sounds like this may not be as unusual a circumstance as I was first thinking! I'm sooo glad to have this forum to get advice from people who are more experienced than me. It makes navigating through it all much easier.